p53 localization and its interaction with Bcl-XL. (A) Localization of p53 in OCI-AML-3 and MOLM-13 cells. Cells were treated with 10 μM Nutlin-3a for 3 hours. Cells were fixed, stained for p53 (green) and mitochondrial marker protein cytochrome c oxidase IV (red), and visualized by confocal microscopy. Localization of p53 to mitochondria is indicated by the yellow-orange color in the merged images. (B) OCI-AML-3 and MOLM-13 cells were incubated with 10 μM Nutlin-3a for 6 hours, and untreated (–) or treated (+) cells were immunoprecipitated with anti-p53 or anti–Bcl-XL antibodies and immunoblotted for Bcl-XL or p53. Immunoprecipitation with anti–Bcl-XL followed by p53 blotting showed a specific p53/Bcl-XL complex in both cells. The complex was not detectable in reverse, suggesting that a minor fraction of increased p53 protein might bind to Bcl-XL protein.
